The Japan Meteorological Agency has issued a nationwide heatwave warning for Marine Day on July 20, 2026 [1].
These extreme weather conditions coincide with a public holiday, increasing the risk of heat-related illness for millions of people traveling or attending outdoor events across the archipelago [1].
Forecasters expect temperatures to reach 36°C in both Tokyo and Nagoya [1]. In Kumagaya, located in Saitama Prefecture, the heat is expected to be even more intense with a forecast high of 38°C [1]. Many other cities across the eastern and western regions are predicted to see temperatures in the 35°C to 36°C range [1].
The heat is expected to intensify throughout the week. Forecasters predict that temperatures in Nagoya could climb as high as 40°C by mid-week [1].
Beyond the heat, atmospheric conditions are creating volatility in other regions. Weather services said sudden inland thunderstorms could develop rapidly during the afternoon [1]. These localized storms often bring heavy rain and unpredictable wind patterns, posing a challenge for holiday commuters.
In the north, the situation is more critical due to precipitation. Authorities have issued warnings for Hokkaido, where heavy rain is expected to create a significant risk of landslides [1]. This rain-induced instability in the soil makes mountainous areas particularly dangerous for residents and visitors.
The agency said the combination of seasonal summer heat and specific atmospheric pressures is driving the rapid temperature increases seen in the afternoon [1].
“Temperatures are expected to reach 36°C in both Tokyo and Nagoya.”
The convergence of a national holiday with extreme heat and landslide risks creates a complex public safety challenge. While the heatwave affects the urban centers of Tokyo and Nagoya, the geological risks in Hokkaido require a different emergency response, highlighting the diverse climatic threats Japan faces during the peak of the summer season.
